The blue and white selectable markers have been developed which differentiate recombinant colonies from non-recombinant colonies on the basis of their ability to produce colour in the presence of a chromogenic substrate.
Given below are two statements about this method:
Statement I : The blue coloured colonies have DNA insert in the plasmid and they are identified as recombinant colonies.
Statement II : The colonies without blue colour have DNA insert in the plasmid and are identified as recombinant colonies.
In the light of the above statements, chocse the most appropriate answer from the options given below:
- A
Statement I is incorrect but Statement II is correct
- B
Both Statement I and Statement II are correct
- C
Both Statement I and Statement II are incorrect
- D
Statement I is correct but Statement II is incorrect
In blue-white screening, the recognition site for the restriction enzyme lies within the coding region of the -galactosidase gene. When foreign DNA is inserted, the gene gets disrupted — this is called insertional inactivation.
Consequences:
- Recombinant colonies — insert present, -galactosidase inactive, no colour in presence of chromogenic substrate white colonies.
- Non-recombinant colonies — no insert, -galactosidase active blue colonies.
Hence Statement I is incorrect (blue = non-recombinant, not recombinant) and Statement II is correct.
Practice more Biology
Concept-wise practice with instant solutions on Fundamenthol.
Start practicing →